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Topic 4 · Biodiversity and Natural Resources

Topic 4 · Biodiversity and Natural Resources — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

20 min read 31 parts Lesson 1 of 22 Unit quiz

📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision
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Lesson summary

Biodiversity and Natural Resources — notes: Explain levels of biodiversity and threats to it, how to measure and compare biodiversity, niches and adaptation, natural selection, Hardy-Weinberg, speciation, classification, conservation, plant structure and fibres, drug testing, an…

  • Three levels
  • Habitat diversity
  • Species richness and diversity
  • Genetic diversity
  • Between populations
  • Importance

Part 1 of 28Levels of biodiversity

Biodiversity
  • Biodiversity variation within and between all forms of life: the range and variety of genes, species and habitats in a region;
    • it makes ecosystems resilient.
Three levels
  • Ecosystem or habitat diversity.
  • Species diversity (number of species and relative abundance).
  • Genetic diversity within each species.
Habitat diversity
  • Habitat diversity many habitats means high biodiversity; a large sandy desert has few and low biodiversity.
    • (coral reefs have many microhabitats and niches)
Species richness and diversity
  • Species richness is the number of species (a rainforest is species-rich).
  • Species diversity also includes the abundance of each species.
  • Many species with some very rare does not mean high diversity.
Stability
  • Stability high species diversity gives resilience;
    • Florida pine forests dominated by one or two species could collapse if a pathogen kills a dominant tree.

Part 2 of 28Genetic diversity and endemism

Genetic diversity and endemism
Genetic diversity
  • Genetic diversity diversity of alleles and genes in a species' genome;
    • measured by the proportion of genes with more than one allele and the number of alleles per gene.
Between populations
  • Between populations differences arise from different selection pressures changing allele frequencies in slightly different ranges;
    • also found within a single population.
Importance
  • Importance helps a population adapt to changes in biotic factors and abiotic factors (temperature, humidity, rainfall).
    • (predators, pathogens, competition)
Small isolated populations
  • Small isolated populations inbreeding makes many individuals homozygous, lowering diversity and making recessive genetic diseases more common.
Endemic species
  • Endemic species occur naturally in only one area; at particular risk of extinction.
    • (pygmy three-toed sloth on a small island off Panama)

Part 3 of 28Modern farming, climate change and ocean effects

Modern farming, climate change and ocean effects
Changes after World War II
  • Changes after World War II monoculture, cereals not vegetables, larger fields, wetlands drained and ponds filled, much more fertiliser and pesticide.
    • (hedgerows and stone walls removed)
Effects on biodiversity
  • Monocultures support far less biodiversity than natural habitats or natural grazing land.
  • Hedgerow loss removes habitat and nesting sites for insects, small mammals and birds.
  • Fertilisers leach into waterways causing eutrophication and deaths of invertebrates and fish.
  • Pesticides kill non-target species including pollinators such as bees.
Climate change
  • More extreme weather (hurricanes, typhoons, floods, droughts); possibly too fast for species to adapt.
  • Species move to poles or higher altitude and may be outcompeted or outcompete others, both lowering biodiversity;
    • plants may not move fast enough.
  • Ocean acidificationmore CO2 dissolves in seawater, lowering pH and harming shell formers (plankton, coral polyps).
  • Coral bleaching
    • warmer water makes symbiotic organisms leave;
      • corals die and reefs, and their biodiversity, are lost.

Part 4 of 28Measuring species diversity in a habitat

Habitat and community
  • Habitat and community a habitat can be big (grassland) or small (puddle);
    • a community is interacting populations of different species in one place.
Species richness
  • Species richness number of species;
    • simplest measure but misleading because it ignores numbers of individuals.
Species abundance
  • Species abundance relative numbers of individuals per species;
    • two areas with 4 tree species have equal richness but the one dominated by a single species with one rare species has lower diversity.
Index of diversity
  • Index of diversity used by conservationists because it takes species number and evenness into account.
Species lists
  • Species lists possible for small areas or large species like trees;
    • large ecosystems need sampling to estimate.

Part 5 of 28Sampling methods

Quadrats
  • Quadrats square frames (for example 0.25 m2 or 1 m2) for plants; lay randomly to avoid bias; record abundance or percentage cover (totals can be over or under 100%).
    • (grid with numbered squares and random number generator)
Equipment for animals
  • Sweep netsfine strong nets for flying insects and insects in long grass.
  • Pitfall trapsburied cans or jars catching ground-dwelling, often nocturnal, invertebrates.
  • Kick samplingnet on a stream bed facing the flow while the stream bed above is churned by foot for a set time.
Reliability
  • Reliability take as many samples as possible;
    • use the same method when comparing habitats;
    • results estimate total individuals or richness.

Part 6 of 28Genetic diversity measures

Genetic diversity measures
Genetic diversity
  • Genetic diversity allele variety in a gene pool; useful to track changes over time or compare species.
Phenotype
  • Phenotype a greater variety of phenotypes suggests higher genetic diversity.
Genotype
  • Genotype sequence DNA; more alleles for a characteristic means more diversity.
Heterozygosity index
  • H = number of heterozygotes ÷ number of individuals.
  • Pea plants
    • 350 Rr out of 620;
      • H = 350 ÷ 620 = 0.56.
  • Calculate H at many loci and average to estimate genome-wide diversity.

Part 7 of 28Index of diversity calculation

  • Formula
    • D = N(N – 1) ÷ Σn(n – 1), where N is the total number of organisms and n the number of one species;
      • a larger D means more diversity.
Index of diversity calculation
Calculate N(N – 1) (value A).
Calculate n(n – 1) for each species and add them (value B).
Divide A by B.
Worked example
  • Worked example garden insects of 9 species with counts 7, 34, 6, 21, 12, 37, 7, 19, 59.
  • N = 202; N(N – 1) = 202 × 201 = 40 602.
  • Σn(n – 1) = 6 884.
  • D = 40 602 ÷ 6 884 = 5.90.
Use
  • Use compare habitats; you need to use the formula and interpret D, not memorise it.

Part 8 of 28Niches and adaptations

Habitat and niche
  • Habitat and niche habitat is where a species lives; niche is its role: biotic interactions and abiotic interactions (gas exchange).
    • (what it eats and what eats it)
One species per niche
  • One species per niche competition for the same niche makes one species win;
    • the other moves to a slightly different niche or goes extinct locally.
Example
  • Example three North American warbler species in spruces feed at different heights, so they coexist.
Adaptations
Adaptations increase survival and reproduction.
  • Anatomicalstructural (horns, claws, feathers).
  • Behaviouralcourtship, defence.
  • Physiologicalprocesses (venom production, digesting cellulose).
Requirement
  • Requirement adaptation to both biotic and abiotic conditions to occupy a unique niche.

Part 9 of 28Natural selection

Variation
  • Variation between species (interspecific) and within a species (intraspecific);
    • partly from random mutations producing new alleles and so different phenotypes.
Selection pressures
  • Selection pressures environmental factors that make survival difficult.
    • (predation, disease, competition)
1
Variation exists in the population.
2
Selection pressures favour individuals with certain phenotypes.
3
These survive and reproduce, passing on the advantageous alleles.
4
Individuals without them mostly die before reproducing, reducing competition.
5
Over generations the frequency of advantageous alleles rises and others fall, leading to evolution.
  • Evidence
    • Darwin's theory gained acceptance as evidence accumulated; the peppered moth is a well-known example.

Part 10 of 28Hardy-Weinberg

Hardy-Weinberg
Principle
  • Principle allele frequencies stay the same between generations if mating is random, the population is infinitely large,
    • and there is no migration, mutation or natural selection.
Change in frequencies
  • Change in frequencies shows that migration, mutation or selection has occurred.
Genotypes
  • BB, Bb, bb; frequencies are proportions of the population (total 1).
Equations
  • Equations p + q = 1; p2 + 2pq + q2 = 1.
    What the symbols mean: p = frequency of the dominant allele · q = frequency of the recessive allele · p2 = homozygous dominant · 2pq = heterozygous · q2 = homozygous recessive
  • p2: homozygous dominant.
  • 2pq: heterozygous (from either parent).
  • q2: homozygous recessive.
Worked example
  • 10% white-feathered (ff).
  • q2 = 0.10, so q = 0.32.
  • p = 1 – 0.32 = 0.68.
  • p2 = 0.46; 2pq = 2 × 0.68 × 0.32 = 0.44.
  • Check0.46 + 0.44 + 0.10 = 1.
Method
  • Method start with the recessive phenotype (genotype known);
    • the equations estimate frequencies, the principle describes equilibrium.

Part 11 of 28Reproductive isolation and speciation

Reproductive isolation and speciation
Species
  • Species organisms with shared characteristics that produce fertile offspring.
Reproductive isolation
  • Reproductive isolation changes in alleles and phenotype stop some individuals breeding with others.
  • Seasonaldifferent mating or flowering times.
  • Mechanicalreproductive parts no longer match.
  • Behaviouralcourtship no longer attracts mates.
Causes
  • Causes geographical barriers or random mutations producing new alleles.
Speciation by geographical isolation
  • Speciation by geographical isolation a barrier stops gene exchange; different selection pressures and mutations alter gene pools; populations diverge physiologically, behaviourally and anatomically and become separate species.
    • (water, mountains, motorway)
Time
  • Time speciation takes a very long time.

Part 12 of 28Classification and the binomial system

Taxonomy
  • Taxonomy classification of species into hierarchical, non-overlapping groups (taxa) based on evolutionary relationships (phylogenetic).
Ranks, lowest to highest
  • Ranks, lowest to highest species, genus, family, order, class, phylum, kingdom, domain;
    • mnemonic Kings Play Chess On Fancy Gold Squares for kingdom to species.
Higher ranks
  • Higher ranks contain more organisms with less similarity.
Species concept
  • Species concept similar species in a genus remain separate because they cannot produce fertile offspring.
Early systems
  • Early systems used phenotype, which can mislead; DNA sequencing now shows evolutionary relationships.
    • (whales and sharks look similar)
Binomial
  • Binomial genus (capital) then species (lower case), italicised or underlined, in Latin: Homo sapiens, Canis familiaris;
    • universal names.

Part 13 of 28Five kingdoms

KingdomFeatures
Prokaryotae (Monera)Prokaryotic cells with no nucleus; typically under 5 µm; example bacteria causing pneumonia
ProtoctistaEukaryotic, very diverse, usually aquatic; single cells or groups; protozoa have animal-like cells with no wall; algae have plant-like cells with cellulose walls and chloroplasts
FungiEukaryotic; non-cellulose (chitin) walls; saprotrophs digesting extracellularly or parasites; spores; unicellular (yeast) or hyphae forming mycelium with fruiting bodies; moulds, yeasts, mushrooms
PlantaeMulticellular eukaryotes; cellulose walls; large permanent vacuoles; differentiate into tissues and organs; chloroplasts (not in all cells); autotrophs; mosses, ferns, flowering plants
AnimaliaMulticellular eukaryotes; differentiate into tissues and organs; small temporary vacuoles; no cell walls; heterotrophs with varied feeding; molluscs to mammals

Part 14 of 28Three domains and molecular phylogeny

Three domains and molecular phylogeny
Limits of physical features
  • Limits of physical features colour, shape and size can cause wrong classification.
Genome sequencing and immunology
  • Genome sequencing and immunology led to reclassification as knowledge changes.
Three-domain system
  • Three-domain system based on molecular analysis of RNA genes: Archaea (prokaryotes), Bacteria (prokaryotes) and Eukarya (eukaryotes).
Molecular phylogeny
  • Molecular phylogeny compares DNA, RNA or proteins; more similar molecules mean a more recent common ancestor.
Finding
  • Prokaryotae split into Archaea and Bacteria, which are less closely related than thought;
    • the other four kingdoms are in Eukarya.
Lesson
  • Lesson cell type alone is insufficient to classify organisms.

Part 15 of 28Conservation: in situ and seed banks

Extinction
  • Extinction reduces biodiversity; endangered species are threatened with extinction.
In situ
  • In situ natural habitat with all support systems.
    • (national and marine parks)
Captive options
  • Captive options zoos, botanic gardens, frozen zoos and seed banks.
Seed bank
  • Seed bank dried seeds stored in temperature-controlled conditions;
    • seeds of one species from different sites to maintain genetic diversity;
    • regrown periodically to refresh stock.
  • Svalbard Global Seed Vault, Arctic Circle, almost 1 million seed samples;
    • many organisations deposit crop seeds.
  • Coffee and cocoa seeds cannot be frozen, so successive generations or tissue cultures are kept.
Advantages
  • Supports research on growing plants from seed.
  • Stocks of useful plants (medicinal, crop), reducing pressure on wild populations.
  • Education and community involvement (local seed banks).
Limitation
  • Limitation small genetically limited samples may not represent wild populations.

Part 16 of 28Conservation: zoos and reintroduction

Zoos
  • Zoos captive breeding for release;
    • research on genetics, behaviour, habitat needs and nutrition;
    • education that builds public enthusiasm.
Problems
  • Small breeding populations lose genetic diversity.
  • Some animals will not breed in captivity.
  • Not all zoos give suitable habitats.
  • Ethical objections.
  • Zoo behaviour may differ from the wild, affecting data reliability.
Examples
  • Examples the oryx was saved and reintroduced in Africa;
    • pandas have been bred for over 60 years with none reintroduced.
Reintroduction benefits
  • Reintroduction benefits prevents wild extinction, helps dependent organisms, restores degraded habitats.
Reintroduction risks
  • Reintroduction risks new diseases; animals may lack skills to find food or communicate.

Part 17 of 28Plant cell structure

Plant cell structure
Cell wall
  • Cell wall outside the cell membrane, cellulose gives support.
Middle lamella
  • Middle lamella outermost layer, glues neighbouring cells together and gives stability.
Plasmodesmata
  • Plasmodesmata cytoplasm threads linking neighbouring cells for transport and communication.
    • (lined by membrane)
Pits
  • Pits thin regions of the wall, lined up in pairs between cells, facilitating transport.
Chloroplasts
  • Chloroplasts larger than mitochondria with a double membrane;
    • thylakoids with chlorophyll stack into grana joined by lamellae;
    • photosynthesis in the thylakoid membranes and stroma;
    • contain circular DNA and ribosomes.
Amyloplasts
  • Amyloplasts small membrane-bound organelles storing starch granules, converting it back to glucose when needed.
Vacuole and tonoplast
  • Vacuole and tonoplast sac of cell sap with a selectively permeable tonoplast; keeps cells turgid (prevents wilting) and isolates or breaks down unwanted chemicals.
    • (water, minerals, waste, enzymes)

Part 18 of 28Xylem, sclerenchyma and phloem

1Xylem vessels
  • Xylem vessels transport water and dissolved minerals; support.
  • Lignin in walls withstands the pressure of the water column.
  • Long hollow tubes of dead cellsno cytoplasm or organelles to slow flow.
  • Unlignified pits allow lateral movement between vessels.
2Sclerenchyma fibres
  • Sclerenchyma fibres support only;
    • dead cells forming long hollow tubes with end walls;
    • lignified but no pits;
    • extra cellulose.
3Phloem
  • Phloem transports assimilates (mainly sucrose) from sources (leaves) to sinks (roots) in either direction (translocation);
    • no support role.
  • Sap is the dissolved organic compounds.
  • Sieve tube elements are the main conducting cells, joined end to end with sieve plates and no lignin.
  • Companion cells have nuclei and cytoplasm, control the metabolism of the sieve tube element and load/unload sugars.
  • Also parenchyma (storage) and strengthening fibres.
  • Mature phloem contains living cells.
4Vascular bundles in stems
  • Vascular bundles in stems xylem towards the middle, phloem nearer the outside, with sclerenchyma fibres for extra support.

Part 19 of 28Water and mineral ions in plants

SubstanceImportance
WaterNeeded for photosynthesis; transport medium for minerals; turgidity through vacuole pressure; temperature regulation so enzymes work optimally
Magnesium ionsNeeded to make chlorophyll (green colour, photosynthesis)
Nitrate ionsNeeded to make DNA, proteins (including enzymes) and chlorophyll; essential for growth, fruit and seeds
Calcium ionsImportant cell wall components; needed for proper growth
  • Uptake
    • through root hairs, travelling up in xylem; deficiency causes yellow leaves and stunted growth.

Part 20 of 28Practical: mineral deficiency

  • Apparatus
    • nutrient broths, test tubes, seedlings, aluminium foil, balance.
1
Prepare three nutrient broths with all minerals but high, medium or low calcium.
2
Label nine tubes (three of each).
3
Use nine seedlings of the same plant and age and record each mass.
4
Suspend one seedling's roots in each tube.
5
Cover tubes with foil to keep light from the broth.
6
Leave near light for a few days.
7
Blot each plant dry and measure the mass again.
8
Calculate the mean change in mass per broth and note physical differences.
  • Variation
    • broths lacking one mineral completely, with two controls: one with all minerals and one with none.

Part 21 of 28Starch and cellulose

Starch and cellulose
Starch
  • Starch plant storage polysaccharide in granules in plastids;
    • takes longer to digest than glucose;
    • compact and insoluble.
    • (no osmotic effect; otherwise cells would need thicker walls)
  • Amylose (10–30%): unbranched helix of α-glucose with 1,4 bonds; compact and resistant to digestion.
  • Amylopectin (70–90%): 1,4 and 1,6 bonds, branched;
    • many terminal glucose molecules for rapid hydrolysis or storage.
Cellulose structure
  • Cellulose structure long chains of β-glucose joined by 1,4 glycosidic bonds;
    • each β-glucose is rotated 180° to the next;
    • many hydrogen bonds between parallel chains (microfibrils) give great strength.
Cellulose function
  • Cellulose function main structural component of cell walls;
    • high tensile strength lets walls resist turgor pressure;
    • with other molecules (lignin) forms a strengthening matrix.

Part 22 of 28Plant fibres and their strength

Plant fibres and their strength
Sclerenchyma fibres and xylem vessels
  • Sclerenchyma fibres and xylem vessels long hollow dead cells.
    • (often from lignification, which stops substances entering or leaving)
Uses
  • Uses rope and fabrics (cotton, hemp).
Strength comes from
  • Mesh-like arrangement of cellulose microfibrils.
  • Secondary thickening producing a thick secondary wall, often with lignin.

Part 23 of 28Practical: tissue types in stems

Practical: tissue types in stems
Slides
  • Slides pre-prepared permanent slide, or stain a thin cross-section.
Apparatus
  • Apparatus plant stem, scalpel, stain, slide, coverslip, forceps, dissecting needle, light microscope.
1
Cut a very thin cross-section with a scalpel.
2
Place in stain (toluidine blue O) for one minute: xylem and sclerenchyma blue-green, phloem pinkish purple.
3
Rinse in water and mount, lowering the coverslip slowly from one side to avoid trapping bubbles.
4
View and focus.
5
Make a labelled drawing of the positions of xylem vessels, phloem sieve tubes and sclerenchyma fibres.

Part 24 of 28Practical: tensile strength of fibres

Tensile strength
  • Tensile strength the maximum load a fibre carries before breaking.
Apparatus
  • Apparatus plant fibres, retort stand, clamp, weights.
1
Clamp one end of the fibre to the stand.
2
Hang a weight on the other end.
3
Add weights one at a time until the fibre breaks.
4
Record the mass at breaking: this is the tensile strength.
5
Repeat with more samples and calculate the mean.
  • Controls
    • same fibre length and all other variables constant.

Part 25 of 28Development of drug testing

1Clinical trials
  • Clinical trials new drugs are tested for effectiveness and side effects before sale.
2Historical example
  • William Withering (1700s) treated dropsy with foxglove extract containing digitalis; foxglove is poisonous,
    • (swelling from heart failure)
  • so he made different concentrations and experimented on patients to find the most effective safe concentration.
    • ("digitalis soup")
3Modern sequence
  • Computer modelling.
  • Tests on human tissue in the lab.
  • Tests on animals.
  • Clinical trials with human subjects.
PhasePurpose
1Small group of healthy people: reaction, side effects and correct dose
2Larger group of patients: effectiveness; placebos often used
3Large group of patients split between the new drug and an existing drug to compare
1Placebo
  • Placebo looks like the drug but has no active ingredient;
    • patients do not know which they get;
    • the placebo effect is improvement due to belief.
2Double blind
(phases 2 and 3) — neither patient nor doctor knows who receives the drug, reducing bias.

Part 26 of 28Practical: antimicrobial properties of plants

Antimicrobial
  • Antimicrobial kills microbes or prevents their growth;
    • bacteria need nutrients, oxygen (aerobic), and suitable temperature and pH for enzymes.
Apparatus
  • Apparatus broth with bacterial culture, agar plate, pipette, spreader, plant tissue, pestle and mortar, ethanol, funnel, beaker, filter paper, forceps, incubator.
1
Transfer bacteria from the broth to an agar plate with a sterile pipette and spread evenly, opening the lid as little as possible and replacing it at once.
2
Dry and finely grind plant tissue; soak in ethanol to extract antimicrobial substances; filter.
3
Dip equal sterile paper discs in the extract with sterile forceps for the same time; the control disc is dipped in ethanol only.
4
Space discs evenly, tape the lid, invert the plate and incubate at 25 °C for 24–48 hours.
Incubation at 25 °C
  • Incubation at 25 °C good bacterial growth without encouraging human pathogens.
Analysis
  • Analysis larger clear zone means a more effective extract;
    • measure diameter (nearest mm) or area (π r2, radius half the mean diameter);
    • repeat at least three times and average.
Aseptic technique
  • Keep windows and doors closed.
  • Disinfect surfaces and utensils.
  • Use sterile equipment and discard afterwards.
  • Work near a Bunsen flame so rising hot air draws microbes away.
  • Hold the flame near the neck of the broth container when opening or closing.
Control
  • Control the ethanol disc shows differences are due to the plant extract and not the paper or ethanol.

Part 27 of 28Sustainability and plant materials

Sustainability
  • Sustainability using resources so current needs are met without depleting them for future generations;
    • needs renewable resources (solar energy) rather than finite ones (fossil fuels,
  • which take millions of years to form).
Sustainable practices
  • Sustainable practices minimise environmental damage; unsustainable practices rely on finite supplies (fossil fuels for oil-based plastics).
    • (replant trees after logging)
Plant fibres
  • Use fewer fossil fuels; plants can be replanted.
  • Biodegradable, unlike most oil-based plastics.
  • Easier and cheaper to produce in developing countries than extracting oil.
  • Ropes are typically weaker than plastic ones.
Starch
  • Excess sugar stored as starch can make bioplastics, needing less fossil fuel and from a renewable crop.
  • Can make bioethanol fuel, more sustainable than fuels from oil.

Part 28 of 28Worked examples

  1. Calculate the index of diversity for samples of 5, 3 and 2 individuals of three species. [3]3 marks

  2. Explain why species richness alone is a poor measure of biodiversity. [2]2 marks

  3. Describe how you would investigate the antimicrobial properties of a plant extract. [5]5 marks

  4. Explain the purpose of a double blind trial and a placebo. [3]3 marks

  5. Explain how the structure of xylem vessels suits their function. [4]4 marks

Key terms

TermMeaning
Species richnessThe number of species in a community.
Index of diversityA measure combining species number and abundance, D = N(N – 1) ÷ Σn(n – 1).
Heterozygosity indexThe number of heterozygotes divided by the number of individuals in a population.
NicheThe role of a species in its habitat, including biotic and abiotic interactions.
Endemic speciesA species found naturally in only one area.
BinomialA two-part Latin species name made of the genus then the species.
Seed bankA facility that stores dried seeds to conserve plant diversity.
Tensile strengthThe maximum load a fibre can carry before breaking.
Double blind trialA trial in which neither patients nor doctors know who receives the drug or placebo.

Avoid these mistakes

1
Using species richness and species diversity as if they mean the same — diversity also includes abundance.
2
Putting the genus in lower case or not italicising a binomial — genus capital, species lower case, both italicised.
3
Saying plant stems have xylem on the outside — xylem is towards the middle, phloem nearer the outside.
4
Forgetting a control disc soaked only in ethanol in antimicrobial investigations.
5
Saying Hardy-Weinberg works only if natural selection is occurring — the principle requires no selection, migration or mutation.

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